I just answered a similar question with the following...
I had luck with the Climber Selection Bar extension. You select "Field" for the List type parameter, your dimension for the Field parameter and set your function for the Initial selection parameter (both setting a static string and using the max function on a dimension worked for me). You can also hide the "list" by unchecking the Visible checkbox.
This worked best for me by placing a couple of these on a separate sheet (e.g. the first sheet that the user should click on).